This article presents a mixed hardware-software approach for balancing security and performance of cryptographic computations in embedded systems. The authors assume that the system employs elliptic-curve cryptography (ECC) for data protection. Specifically, they consider ECC based on elliptic curves over prime fields recommended by the National Institute of Standards and Technology (NIST). The authors study a system prototype that uses a flexible hardware processor for accelerating expensive ECC computations. Their approach supports multiple levels of security and performance, which allows the system to adapt to different application requirements.